The present invention relates to a prosthetic ring for heart surgery, particularly for mitral, tricuspid, or aortic annuloplasty.
In normal mitral, tricuspid, or aortic valves, the valves overlap at the center of the fibromuscular ring that surrounds the valve, ensuring that the valve prevents backflow of blood from the ventricle to the atrium or from the aorta to the ventricle. Various diseases can cause deformation or dilation of these rings, causing a leak in the valves and, hence, backflow of blood. As long as ring deformation is not too great, it is preferable to surgically reconstruct the ring rather than replace the total valve.
A prosthetic ring designed for this purpose includes a core covered with a sheath of blood-compatible textile material. The core must have sufficient rigidity to reduce deformation or dilation of the biological ring without disturbing, to the extent possible, the natural opening and closing movements of the valve. The sheath allows the prosthesis to be sutured to the wall of the heart or aorta.
Several prosthetic ring models have been developed in the last two decades.
The earliest implants, described, for example, in U.S. Pat. No. 3,656,185 to Carpentier, are annular or partially annular rigid implants. The rigidity of these rings allows dilation of the biological ring to be reduced and restores a satisfactory shape to it, but, on the other hand, has the drawback of resisting the natural flexibility of the ring of the posterior mitral valve and the tricuspid septal valve, which can lead to dysfunction of these valves. In addition, these rigid-ring prostheses offer resistance to the natural movements of the wall of the heart, so that sutures in the heart wall are stressed and hence subjected to wear and stretching.
On the other hand, certain designers have proposed extremely flexible prosthetic rings, such as those described in U.S. Pat. No. 4,290,151 to Massana, and in the papers by Duran published in the journal "The Annals of Thoracic Surgery," Vol. 22, No. 5, 458-463 (1976). U.S. Pat. No. 4,042,979 to Angell also proposes a flexible ring, which can be adjusted during surgery to a desired geometry. These highly flexible rings allow too much fibromuscular ring deformation and do not always restore satisfactory coaptation of these valves.
U.S. Pat. No. 4,489,446 to Reed describes a ring composed of two nested rigid elements, which slide into each other upon each contraction of the heart, allowing the ring to deform in its plane. This ring has the drawbacks of 1) being too rigid and 2) resisting heart movements perpendicular to the plane of the ring.
More recently, prosthetic rings with portions of different rigidities at their circumference have been proposed.
U.S. Pat. No. 4,917,698 to Carpentier describes a prosthetic ring, composed by assembling two segments for a mitral valve and three segments for a tricuspid valve. The segments are connected to each other and articulated with each other by means of a flexible textile link that passes through them. One of the segments of this ring is rigid and made of titanium alloy, while the other segment or segments is/are flexible and made of a synthetic material known as DELRIN. Several flexible segments with different dimensions can be connected to one rigid segment to constitute a ring, to allow the flexibility of the flexible portion of the ring to be modulated, as needed.
U.S. Pat. No. 5,061,277 to Carpentier and Lane describes another ring having a rigid part made of a titanium alloy and a flexible silicone part. These parts are also connected together by a flexible link made of a textile material. In both cases, this link has the drawback of possibly being subject to wear and thus affecting, over time, the strength of the implant.
U.S. Pat. No. 5,104,407 to Lam, Nguyen, and Carpentier describes a ring having an inner part made of a spiral winding of fine fibers of a cobalt-nickel alloy known under the trademark ELGILOY. The various layers of fibers overlap in a rigid part and are separated from each other by an elastomeric material in a more flexible part. The number of fiber layers varies according to the elasticity to be obtained. This structure allows better distribution, over the periphery of the ring, of the stresses exerted by the heart muscle. Because of its structure, however, this ring appears to be difficult to deform, other than in its plane, while the biological ring is also subjected to deformation perpendicular to its plane. The rigidity in this direction also interferes with certain components of the natural heart movement. Moreover, this ring appears to be complex and difficult to manufacture.